Klinefelter Syndrome (47,XXY-Syndrom) [Q98.0]
Dipl.-Biol. Uwe Heinrich
The Klinefelter syndrome has an incidence of approx. 1:1,000 in male newborns. Approximately 80% of all patients exhibit a pure 47,XXY karyotype, the remaining 20% exhibit mosaicisms or other X polysomies. During childhood discreet abnormalities in psychomotor development as well as passivity and learning difficulties may occur. During puberty, a hypergonadotropic hypogonadism with an underdevelopment of the secondary sexual characteristics, azoospermia, as well as a tall stature with accumulation of abdominal fat and possibly a gynecomastia are developing. In later stages, osteoporosis may occur. The intelligence is usually within the norm or 5-10 IQ points below the average of the family. From puberty on testosterone replacement therapy is indicated if subnormal serum testosterone levels are encountered in order to reduce the risks of long-term complications such as osteoporosis.